A. Field of the Invention
The present invention relates to a damper mechanism, and particularly a damper mechanism for transmitting a torque and damping a torsional vibration.
B. Description of the Background Art
A damper mechanism is a device used in a power transmission device for transmitting torque and for absorbing and damping a torsional vibration transmitted with the torque. The damper mechanism is incorporated in a clutch disk assembly of a clutch, a flywheel assembly or the like used in an automobile. The damper mechanism is basically formed of a first rotary member, a second rotary member and elastic members such as springs which are arranged between the first and second rotary members. The elastic members are compressed between the first and second elastic members when these members rotate relatively to each other.
The clutch disk assembly is basically formed of a clutch disk having friction facings, a pair of circular plate members fixed to the clutch disk, an output hub having a flange which is arranged between the circular plate members, and torsion springs for elastically coupling the flange to the circular plate pair in the circumferential direction. In this structure, a damper mechanism is formed of the circular plate member pair, the flange of the hub and the torsion springs.
Each torsion spring is a coil spring, and is disposed in a window or opening which is formed in the flange. Each of the circular plate members is provided at portions corresponding to the windows or the torsion springs with accommodating or retaining portions, which are axially expanded or are partially cut and bent axially outward. The retaining portions of the paired circular plate members restrict the radially and axially outward movements of the torsion springs.
When the clutch is engaged, the clutch disk assembly rotates together with a flywheel. A centrifugal force produced thereby moves the torsion springs radially outward, and forces them into contact with the radially outer sides, e.g., of the retaining portions of the circular plate members. When a torsional vibration is transmitted to the damper mechanism in the above state, the torsion springs are repeatedly compressed and restored so that they slide with respect to the retaining portions of the paired circular plate members. As a result, either of both of the retaining portions and the torsion springs are liable to wear and break.
In recent years, clutches of automobiles are operated less times owing to development of freeways so that life-times of the clutch disks (friction facings) have increased. Accordingly, the clutch disk assembly can be used until the circular plate member or the torsion spring breaks due to sliding of the spring on the retaining portion of the circular plate member. Accordingly, it is important to reduce wear caused by sliding of the springs for increasing the whole life-time of the clutch disk assembly.
The prior art has employed heat treatment, metal plating or the like for reducing the wear due to sliding of the spring on the retaining portion of the clutch disk assembly. However, these methods sometimes experience premature failure if the treated surface layer becomes worn.